Are VLANs required for Softphone-only systems?

Recently, my organization has installed a new Fortgate 100D Firewall to combat the growing threat of cyber attacks. After installation completed, the call quality on all RingCentral softphone has deteriorated to insufficient call quality. This includes dropped calls, sound cutting out, or completely missed calls due to the softphones not getting alerted a call is coming in.

We run a 100down/100up fiber connection with link failover to a copper cable network. Working with RC has produced few positive results based on what we have found. RC is not the issue, but apparently, my internal network is. We run two HP 2530-24G switches with full data passthrough that should not be causing any QOS issues.

What we have completed already;

Used PingPlotter to record quality issues on client computer using 199.255.120.184 as the target.

Ensured all UDP traffic going to 199.255.120.0/22 and 199.68.212.0/22 have a minimum 450 Kbps.

Set all traffic with DSCP 101110

Ensured sip-helper, sip-nat-trace, and RTP processing are disabled in the FortiGate

Ensured the SIP entry in session-helper is disabled (not present at all)

Ensured all traffic is flowing without issue during and not during phone calls.

It should be iterated that we are not using any Desk Phones, only virtual softphones.

So the question stands; should traffic on computers be somehow separated into different VLANs to account for the RC quality issues we have been experiencing?